21665224 has 32 divisors (see below), whose sum is σ = 47088000. Its totient is φ = 9152640.

The previous prime is 21665221. The next prime is 21665227. The reversal of 21665224 is 42256612.

It is an interprime number because it is at equal distance from previous prime (21665221) and next prime (21665227).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a junction number, because it is equal to n+sod(n) for n = 21665192 and 21665201.

It is not an unprimeable number, because it can be changed into a prime (21665221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1252 + ... + 6700.

It is an arithmetic number, because the mean of its divisors is an integer number (1471500).

Almost surely, 2^21665224 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21665224, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23544000).

21665224 is an abundant number, since it is smaller than the sum of its proper divisors (25422776).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21665224 is a wasteful number, since it uses less digits than its factorization.

21665224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5533 (or 5529 counting only the distinct ones).

The product of its digits is 5760, while the sum is 28.

The square root of 21665224 is about 4654.5917114179. The cubic root of 21665224 is about 278.7753659208.

The spelling of 21665224 in words is "twenty-one million, six hundred sixty-five thousand, two hundred twenty-four".